Many industrial wastes, such as the discardable by-products formed in primary and secondary lead smelting operations and, in particular, the blast furnace slag and matte formed in such operations are contaminated with toxic lead ions (Pb.sup.+2). These toxic lead ions are most often present in such wastes in a form in which they are susceptible, over time and through exposure to the forces of the elements (e.g. wind, rain, heat, etc.), to leaching out from and contaminate the leachate from the wastes. In turn, these leachates (containing the toxic ions) eventually find their way into rivers, streams, lakes and aquifers where, they may pose a potential serious health hazard to living beings.
Over the past decade or so, one of the most important ecological problems facing the industrialized countries, such as the United States, Japan and Western Europe is how to safely dispose of the ever-increasing amounts of industrial wastes that are contaminated with toxic lead ions (Pb.sup.+2), such as the discardable by-products formed in primary and secondary lead smelting operations. Several approaches to solving this problem have been suggested and tried, with only limited success.
In general, these approaches have consisted of mixing the lead-contaminated industrial wastes with appropriate proportions of various hardenable materials such as, for example, Portland Cement alone or together with finely divided siliceous, or siliceous and aluminous material (which react chemically with slaked lime at ordinary temperatures in the presence of moisture to form a strong, slow-hardening cement), sodium silicate together with a setting agent, such as lime calcium chloride, Portland cement, calcium carbonate and mixtures of lime and a silicate or an aluminate and then curing the hardenable material. The lead-contaminated industrial wastes are thereby coated with the hardenable material and encapsulated by it after hardening. The toxic lead ions in the industrial waste are literally trapped in the encapsulating impenetrable hardened material and are, thereby, at least in theory, prevented from leaching out into the environment. Examples of such methods are shown and described over the years in U.S. Pat. Nos. 258,460 to Murphy; 1,816,988 to Potts; 2,044,204 to Brice et al.; 3,096,188 to Maydl; 3,188,221 to Matsuda et al.; 3,449,140 to Chi-Sun Yang; 3,565,648 to Mori et al.; 3,837,872 to Conner; 4,116,705 to Chappell; 4,124,405 to Quienot; 4,149,968 to Kupice et al.; 4,208,217 to Anderson; 4,209,335 to Katayama et al.; 4,306,912 to Forss; 4,318,744 to Dodson; 4,600,514 to Connor; 4,687,373 to Falk et al.; 4,731,120 to Tuutti and, in Japanese Patents 57-20158, 58-79892, 60-231445, 60-231446, 61-48444, 61-48448, 61-48455, 61-48456, 61-48460, 61-48467, 61-48468 and 61-48469.
While these various "encapsulating" methods have in a few special cases and circumstances provided a partial, temporary solution to the problems associated with the safe disposal of lead-contaminated industrial wastes they have not, in general, gained wide usage in the United States and elsewhere for disposal of lead-contaminated hazardous industrial wastes, such as those generated as discardable by-products in primary and secondary lead smelting operations, and, in particular, to the disposal of blast furnace slags and matte. This is because, while the toxic lead ions of the thus-treated hazardous wastes are encapsulated in the solid mass produced by such treatments (or "fixed") and are thereby, at least in theory, rendered "non-leachable", the lead in them in actuality is, as a result of the physical deterioration of the encapsulating hardened material (through long-term exposure to the action of atmospheric agents, e.g., hot air and rain, or as the result of cyclical freezing and thawing in the temperate climates), still partially removable therefrom by water leaching.